/Engine/Plugins/Runtime/GeometryProcessing/Source/DynamicMesh/Public/Operations/SelectiveTessellate.h
the number of new vertices added inside the triangle patch (i.e. exclude vertices added along edges). If InTriangleID is not valid then return FTessellationPattern::InvalidIndex.
int GetNumberOfNewVerticesForTrianglePatch ( const int InTriangleID ) const